One of the problems in plasma etching and deposition is the uniformity of the etch or deposition across the surface of the slice. While it is generally understood that the fundamental plasma properties, such as reactant concentrations, ion density/energy profiles, and plasma sheath potentials, control the dependent variables such as rate, uniformity and anisotropy of a process, these properties are typically not monitored in a commercial plasma reactor. The usual approach to controlling these dependent variables is to monitor and control the independent variables such as gas flows and pressures. They are then correlated to the dependent variables via intuition or some empirical model. While these approaches have been effective, the control of plasma processes would be enhanced by a knowledge of the fundamental plasma properties.
Basically, the only typical plasma characterization tool available on all plasma reactors is an endpoint detection system. This is a spectroscopic tool that looks at the intensity of the plasma at a single wavelength that corresponds to the emission of a reactant or product species in the process. A change in the intensity of this signal indicates a change in the concentration of the specific species, and hence indicates the completion of an etch process. However, this method provides no indication of etching uniformly nor of any of the fundamental plasma properties.